A fundamental problem in genetic research involving cotton (Gossypium hirsutum) is the lack of a rapid and simple method to measure expression of a gene of interest in the cotton fiber cell. Evaluation of the phenotype of genes of interest is useful in designing transgenic plants with desired characteristics. Different genetic parameters may affect the phenotype produced by a gene of interest. For instance, various expression cassettes may regulate the expression of a gene of interest differently, thus changing the resulting phenotype of a transformed plant. One skilled in the art would recognize that an expression cassette may be altered so as to affect a corresponding phenotype. Such alterations include, inter alia: varying the type or length of the promoter and/or including or excluding enhancer elements, ribosomal binding sites, introns, and/or polyadenylation sites. Therefore, to obtain the optimal desired phenotype, transformation using many different variations of an expression cassette into the plant of interest is desirable.
Although methods for the transformation of cotton are known (Umbeck, U.S. Pat. Nos. 5,004,863 and 5,159,135; WO 92/15675, published Sep. 17, 1992), these methods typically have very low transformation efficiencies. Furthermore, these methods require a significant amount of time and greenhouse space to regenerate and identify transformed plants. Therefore much time and effort is expended to identify an expression cassette that produces the optimal desired phenotype.
Cotton is a plant of great commercial importance. One significant product from cotton plants, cotton fiber tissue, is used in the production of textiles. The cotton fiber cells that make up cotton fiber tissue are therefore of great interest. Manipulation of the cotton fiber cell phenotype can produce novel and economically important improvements to cotton fiber tissue and, thus, to textiles. Important qualities of the cotton fiber cell include, inter alia, fiber strength, length, color and debellatio.
Although transient expression has been documented in tobacco, maize and Arabidopsis, (see e.g., Hansen et al., Proc. Natl. Acad. Sci. USA 91: 7603-7607 (1994)), transient expression has never been achieved in such a specialized cell type as cotton tissue fiber cells. The invention presented herein addresses these and other problems.